Overheat sensor. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

 Comments on the article

The described device is a temperature-frequency discrete action converter. By structure, this is an autogenerator, the positive feedback loop of which contains an ultrasonic communication line with a sensitive element included in it. They serve as a polymer self-resetting fuse. Due to the temperature dependence of not only the electrical, but also the acoustic properties of such a fuse, the oscillation frequency of the oscillator changes.

The sensor is designed to work as part of devices for temperature tolerance control of objects located in explosive environments [1], but can also be used in other similar systems, for example, in emergency fire alarm devices. Since the connection of the sensitive element with the electronic unit is acoustic, the current flow in the measuring circuit and the possibility of sparking in the controlled area are excluded.

Main Specifications

response temperature,
°С, no more than ............... 60
Response time, s, not
over ........................10
Output voltage range, V, not less than ................5
Supply voltage, V .........27±3
Consumption current, mA, not more than .......................100

The device consists of a sensitive element included in the break of the sound guide, forming an ultrasonic communication line between the emitting and receiving piezoelectric transducers, a power amplifier, a preamplifier and a feedback circuit connecting the output of the preamplifier to the input of the power amplifier.

The radiating transducer excites acoustic waves in the sound guide, which pass through the sensitive element and reach the receiving transducer, which converts them into an electrical signal. This signal, amplified by the pre-amplifier, is fed through the feedback circuit to the input of the power amplifier. As a result of positive feedback, self-oscillations occur in the system.

The sensitive element of the sensor is made of a material whose acoustic impedance changes sharply at a certain temperature. As a result, an abrupt change in the oscillation frequency occurs, which serves as a signal of overheating. After the cause of overheating is eliminated, the temperature of the sensitive element decreases, the acoustic resistance of the communication line and the oscillation frequency return to their original values ​​- the sensor is again ready for operation.

Fig. 1

The sensor circuit is shown in the figure. A power amplifier is made on transistors VT1-VT4. Its voltage gain is determined by the ratio of the resistances of resistors R6 and R4. An emitting piezoelectric transducer BQ1 is connected to the output of the amplifier; it is acoustically connected to the receiving piezoelectric transducer BM1 through a sound guide and a sensitive element VK1. Capacitors C1 and C4 are separating. Diodes VD1 and VD2 set the bias voltage of transistors VT3 and VT4. The power amplifier is powered by a 20 V voltage regulator on the DA1 chip. Capacitor SZ - filtering in the power circuit.

The pre-amplifier is assembled on the op-amp DA3. Since the power supply of the op-amp is unipolar, with the help of resistors R10, R11 and R13, a bias equal to half the supply voltage is applied to its non-inverting input. Capacitor C6 is a blocking capacitor in the bias circuit. Resistor R12 sets the operating mode of the op-amp. Resistors R14-R16 and capacitor C7 form a negative feedback circuit that sets the gain of the preamplifier. The output of this amplifier is connected to the input of the power amplifier through capacitor C9, which closes the positive feedback circuit. Capacitor SU is separating.

The pre-amplifier is powered by a 15 V voltage regulator on the DA2 chip. Capacitor C5 is a filter element in the power circuit.

The sensing element VK1 is a MULTIFUSE polymer resettable fuse from Bourns [2]. In a cooled state, the structure of the polymer filling it resembles a crystal lattice. When heated, it changes, so when a certain temperature is reached, there is a jump not only in the electrical conductivity of the polymer, but also in its acoustic resistance.

Most of the sensor parts are located on a breadboard with plated holes, the mounting is done with thin insulated wires. The board is placed in a metal case on which piezoelectric transducers are installed. The sensitive element of the sensor is outside and connected to the piezoelectric transducers by a sound guide - a U-shaped elbow made of steel wire with a diameter of 0,8 mm and a length of 1 m. The opposite ends of the sound guide are soldered to the working surfaces of the piezoelectric transducers. The sensitive element is soldered into the gap of the sound guide at the place of its bend.

The sensor uses tantalum oxide capacitors K53-52, it is permissible to use others, for example K53-4. Ceramic capacitors - K10-176 (or KM-3-KM-6). Fixed resistors C2-33 (possible replacement - C2-23, MLT, OMLT). Trimmer resistor - SPZ-39a (or SPZ-37, RP1-48). Diodes KD522B can be replaced with other silicon diodes, for example, from the KD503, KD521 series. KT503G transistors can be replaced by transistors of the same series or silicon devices of other series with similar parameters. KT814G and KT815G can be replaced by transistors of the same series or series KT816 and KT817, respectively. Instead of imported microcircuits L7815, L7820, domestic microcircuits KR142EN8V and KR142EN9A can be used, respectively. Piezoacoustic transducers BQ1, BM1 - unpackaged three-output foreign-made (probable type FML-34.7T-2.9B1 -L). Resettable fuse MF-R025 can be replaced with a similar one from RaychemVTyco or Little Fuse.

Setting up the sensor consists in setting the tuning resistor R16 to such a gain in the positive feedback loop, at which stable generation is observed, and the signal at the output of the power amplifier is sinusoidal with a slight two-sided limitation. By increasing the temperature of the sensitive element VK1, its value is fixed, at which an abrupt change in the oscillation frequency occurs. You should make sure that the frequency returns to its original value when the sensing element cools down. In the author's version of the sensor, the frequency of generated oscillations at a sensitive element temperature of +20 °C was equal to 12,9 kHz, and when the temperature reached +40 °C, it increased abruptly to 85,3 kHz.

Literature

1. Vinogradov Yu. Control of explosive gases. - Radio, 2000, No. 10, p. 37.
2. Bourns MULTIFUSE resettable fuses. - Radio, 2000, No. 11, p. 49-51.

Author: O. Ilyin, Kazan, Tatarstan; Publication: radioradar.net

See other articles Section Power regulators, thermometers, heat stabilizers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive There may be more than a hundred planets in the solar system 27.02.2017 NASA scientists have published a manifesto in which they proposed a new definition of the concept of "planet". If accepted, it would add over a hundred planets to the solar system, including Pluto and our Moon. Scientists led by Alan Stern (Alan Stern) believe that a cosmic body in the solar system does not have to be in the orbit of the Sun to be considered a planet. What matters is the properties of the bodies, not their interaction with the stars. Stern is the lead investigator on the New Horizons mission, which reached the dwarf planet Pluto for the first time in 2015. Pluto was decommissioned as a planet in August 2006 and reclassified as a dwarf planet after Caltech astronomer Mike Brown proposed rewriting the definition of planets. The International Astronomical Union (IAU) has stated that the current definition of a planet in the solar system is: "A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass to become round under its gravitational force, and (c ) has free neighborhoods around its orbit". It was the last condition - the clean vicinity of the orbit - that did not allow Pluto to maintain the status of a planet. Stern is dissatisfied with the limitations that this definition imposes. He believes that it is impossible to listen only to astronomers in such a matter. "...You should really listen to a planetary scientist who knows anything about an object. When we look at an object like Pluto, we don't know what else to call it [if not a planet]." Therefore, Stern and his colleagues rewrote the definition of the planet and submitted it to the IAU for consideration. "A planet is a body of substellar mass that is not fusion-producing and has sufficient gravity to assume a spheroidal shape adequately described by a triaxial ellipsoid, regardless of its orbital parameters." In other words, a planet is a round object in space that is smaller than the stars. The new definition means that our Moon, as well as the moons of other planets - Titan, Enceladus, Europa, Ganymede - will be called planets, including Pluto.

Other interesting news:

▪ Technological forecasts for the next five years

▪ Microphones inspired by insects

▪ Smartphones ZTE Nubia Z5S and Z5S mini

▪ Huawei Watch D with blood pressure monitor and ECG

▪ Laboratory in a vest pocket

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Security and safety. Article selection

▪ article Key well. Tips for the home master

▪ article Where and when was the person who committed the murder in front of witnesses fully acquitted? Detailed answer

▪ article Irga spiky. Legends, cultivation, methods of application

▪ article solar water heater. Encyclopedia of radio electronics and electrical engineering

▪ article Powerful rectifier-limiting diodes of the KD2972 series. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024